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(#) Notification Launches Services or BroadcastReceivers

!!! WARNING: Notification Launches Services or BroadcastReceivers
   This is a warning.

Id
:   `LaunchActivityFromNotification`
Summary
:   Notification Launches Services or BroadcastReceivers
Severity
:   Warning
Category
:   Performance
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   4.3.0-alpha01 (December 2020)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://developer.android.com/guide/topics/ui/notifiers/notifications?hl=en#Actions
See
:   https://d.android.com/r/studio-ui/designer/material/notifications-behavior
See
:   https://developer.android.com/guide/topics/ui/notifiers/notifications?hl=en
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/NotificationTrampolineDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NotificationTrampolineDetectorTest.kt)

Notifications should only launch activities -- that's what users expect
(and has been the guidance in both the Android SDK and Material Design
documentation for a while).

A `Service` or a `BroadcastReceiver` should not be used as an
intermediate, because this can lead to significant performance problems,
and as a result, this will not be allowed in Android 12.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/NotificationTest.java:22:Warning: Notifications should only
launch a Service from notification actions (addAction)
[LaunchActivityFromNotification]
    .setContentIntent(serviceIntent)
     -------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/test/pkg/BroadcastTrampoline.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class BroadcastTrampoline extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // The start below will be blocked
        Intent i = new Intent();
        i.setClassName("test.pkg", "test.pkg.SecondActivity");
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(i);
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/NotificationTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import androidx.core.app.NotificationCompat;
@SuppressWarnings("unused")
public class NotificationTest {
    public void testServices(Context context, String channelId, int id) {
        NotificationManager notificationManager =
                context.getSystemService(NotificationManager.class);
        Intent notificationIntent = new Intent(context, ServiceTrampoline.class);
        PendingIntent serviceIntent = PendingIntent.getService(context, 0, notificationIntent, 0);
        NotificationCompat.Builder builder =
                new NotificationCompat.Builder(context, channelId)
                        .setSmallIcon(android.R.drawable.ic_menu_my_calendar)
                        .setContentTitle("Notification Trampoline Test")
                        .setContentText("Tap this notification to launch a new service")
                        .setPriority(NotificationCompat.PRIORITY_DEFAULT)
                        .setContentIntent(serviceIntent)
                        .setAutoCancel(true);
        Notification notification = builder.build();
        notificationManager.notify(id, notification);
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NotificationTrampolineDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `NotificationTrampolineDetector.testLaunchUnknownService`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("LaunchActivityFromNotification")
  fun method() {
     setContentIntent(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("LaunchActivityFromNotification")
  void method() {
     setContentIntent(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection LaunchActivityFromNotification
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="LaunchActivityFromNotification" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'LaunchActivityFromNotification'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore LaunchActivityFromNotification ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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